304 report — 1859. 



present, to examine the action which such bodies exert upon each other's 

 solubility. This kind of isomorphism and homoeormorpliism may be described 

 by the term heteromeric, first employed by Hermann. Heteromeric homceo- 

 morphism is in part what Laurent termed paramorphism. 



E. Dimorphic and trimorphic substances may be isomorphic with two or 

 three different series of bodies in as many different systems. This isomor- 

 phism may be isomeric or heteromeric. The influence which the bodies of 

 each series would exert upon the solubility of a dimorphic salt would be ex- 

 tremely interesting, and especially as regards the comparative influence of 

 the bodies isomorphic with the most stable form, and those isomorphic with 

 the least stable at different temperatures. 



F. The last category of forms includes the hemimorphous bodies in the 

 sense in which Laurent used that term ; that is substances which resemble 

 each other in composition, but which are only partly similar in form — which 

 have one or two angles alike, but all the others very different. 



The application of this scheme of comparative morphology to the subject 

 of this investigation is so obvious that I need not dwell upon it now. By 

 submitting a salt in solution at different temperatures to the action of suc- 

 cessive quantities of a number of salts, beginning with those which exhibit 

 perfect identity of form, equality of volume, and similarity of composition, 

 and proceeding downwards, as indicated in the preceding scheme, until re- 

 mote indications of resemblance are alone perceptible, I hope to be able to 

 ascertain the general character of the influence which form exerts upon solu- 

 bility. To complete the series, it would perhaps be necessary also to study 

 the action of salts which have no resemblance of any definite character. 



The modification in solubility which a salt undergoes on adding a given 

 quantity of another salt, is not, however, due to form alone; the chemical 

 nature of the molecules engaged has perhaps a larger share in the phenomenon. 

 The results of such a series of experiments as I have just planned would not 

 therefore enable us to determine the influence of form, unless we could 

 eliminate the effect due to chemical action, properly so called. This could 

 only be done by making a series of experiments on the influence of chemi- 

 cal composition, according to a scheme of classification analogous to that 

 sketched out for form. This will consist essentially of the following : — a, 

 influence of a number of the soluble salts which the acid of the salt investi- 

 gated forms with different bases ; b, influence of the soluble salts formed 

 by the base of the salt under investigation, with different acids; c, in- 

 fluence which the salts of sesquioxides exert upon the solubility of the salts 

 of the protoxide of the same metal, and upon the protoxide of other metals, 

 where they do not form recognized double salts ; d, influence which salts 

 of polybasic acids, with one, two, &c. of strong base exert upon the solu- 

 bility of different salts ; e, comparative influence of tribasic phosphate of soda, 

 containing two of soda and one of water, and bibasic phosphate of soda with 

 two of soda, &c. 



I have perhaps discussed the classification which I propose to follow in 

 my experiments sufficiently to make the character and scope of the investi- 

 gation evident, and it now only remains for ine to say a few words of the 

 methods which I propose to employ in order to determine, if possible, the 

 nature of the changes which take place on mixing saline solutions, and in 

 heating a single solution, or a mixture, to a high temperature. 



In the following observations upon the physical phenomena which may 

 be taken advantage of to determine the molecular changes taking place 

 without precipitation when solutions are mingled, I propose to mention 

 those only which as yet I have tried with some hopes of usefulness. There 



